GAS GLAXDS OF SOME TELEOSTEAN FISHES. 217 



glandular epitheliuai {Oi^hichthys miherbis, e. g.), is move primitive 

 oi- more evolved than the condition which we found in the Cod, 

 e. g., is a question I shall not discuss ; I will merely say that there 

 are several reasons for accepting, with de Seabra (31), the latter 

 view. The fact that Ophicht/njs and Anguilla possess a very simple 

 type of glandular epithelium is no objection to this view, since 

 the rete of Cejwla and other genera possessing complex types of 

 epithelixnn is almost as simple. 



The glandular epithelium, as we have seen, may line the whole 

 interior of the bladder (as in many Anguilliformes and freish- 

 water teleosts) or be restricted to a small area of the internal 

 surface {OpMdmm type). The Syngnathus type is more or less 

 intermediate between these two conditions. 



The character of the glandular epithelium varies greatly. The 

 cells composing it may be arranged to form [a) a single unfolded 

 layer {Ab/rus, e. g.) ; (6) a layer thrown into simple or complex 

 folds, so that channels are formed leading from the surface of the 

 glandular epithelium to the bladder lumen {Anguilla, Gobiits, 

 iSi/ngnathus, Trigla, Smaris); (c) a thick mass in which the deeper 

 cells can only commvmicate with the bladder lumen by a system 

 of large or small anastomosing channels (the intercellular lumina) 

 which penetrate the cell-mass and open into the bladder cavity 

 by small apertures situated on the internal surface of the 

 glandular mass {Ophidium, Coris, e. g.). At present neither 

 embrj^ology nor comparative anatomy provides evidence to justify 

 the inference that this massive type of gland epithelium is in all 

 cases derived from the folded condition — the folds on this view 

 being supposed to have become elongated, laterally branched 

 perhaps, closely apposed and fused at intervals to produce the 

 cell-mass penetrated by narrow anastomosing channels. It would 

 gratify me to be able to agree with Reis (64) who states that she 

 is able to trace a complete developmental series of complications 

 in the structure of the gas gland epithelium, the simple unfolded 

 cell-layer forming the starting and the cell mass of Coris, Cejjola, 

 or ^sovf the culminating points of the series; but, as I have already 

 stated, the available embryological and anatomical evidence 

 suggests that the two complex types of folded and massive gas 

 gland epithelia were separately derived from the primitive layer 

 of glandular cells by folding (i. e. the plane of cell-cleavage is 

 always at right angles to the plane of the bladder wall) and bj'' 

 thickening (the plane of cell- cleavage being parallel with the plane 

 of the bladder wall) respectively. It is true that forms of gas 

 gland epithelia occxu- apparently transitional in character between 

 the folded and massive types [Trigla gurnardtcs, Smaris maiorii, 

 6'. vulgaris), but I have supplied leasons for regarding these as 

 glandular epithelia of the folded type which have become 

 secondarily massive in form and so differing from the truly 

 massive glands wliich never pass througli a folded stage in their 

 development. Theie is no reason, however, why certain glands 

 should not be truly intermediate in structure, i. e. in Avhich the 

 cells during development divide simultaneously in planes both 



